There is probably very little likelihood of finding life on Mars today, but things were very different in the past.
Simple forms of life could have taken hold on the Martian surface at a time when life forms were also emerging on earth three to four billion years ago.
The possibility of discovering modern-day Martians was discussed by Harvard palaeontologist Prof Andy Knoll at an Academy Times lecture last night in Dublin.
The lecture was organised by The Irish Times, the Royal Irish Academy and Depfa Bank.
Conditions are probably too harsh on Mars today but there was a "window of opportunity" in the past when liquid water flowed on the Red Planet.
Our knowledge of Mars has been transformed by recent satellite and Lander missions to Mars, stated Prof Knoll, who is Fisher Professor of Natural History at Harvard.
He is also a member of the scientific team overseeing the two Mars rovers, Spirit and Opportunity. Their mission began in January 2004 with a hoped-for minimum 90 Martian days traversing the surface.
Yet the two rovers have been rambling around the Martian surface and sending back data for about 1,000 Martian days each, Prof Knoll said.
"I am interested in what the rocks tell us about the past," Prof Knoll said.
"The physical chemistry of the surface tells us that water was more available three to four billion years ago, about the time life emerged on earth."
Yet even at that time there were stark differences between the two planets. Mars had water but much of it would have been highly acidic. Conditions would have been much more severe than on earth, with significantly less water.
If life emerged on Mars it would have had to struggle in such conditions.
"The window of opportunity was closing," Prof Knoll suggested.
Although mission controllers and the public were anxious to find definitive signs of past or current life, the goal of the rover mission was to learn more about Mars's environmental history, something that would indicate whether life might have existed, Prof Knoll pointed out.
